The present invention relates to printable films. In a particular aspect, the invention relates to films that are receptive to solvent-based inkjet inks and methods of printing onto such films. In particular, the present invention relates to melt-processed films that are receptive to solvent-based inkjet inks and methods of printing onto such films to make a graphic suitable for application on vehicles or buildings. A variety of graphics for advertising and promotional displays may be produced. The invention further relates to a method of applying a graphic.
A variety of print methods have been employed for imaging various sheet materials. Commonly employed print methods include gravure, off-set, flexographic, lithographic, electrographic, electrophotographic (including laser printing and xerography), ion deposition (also referred to as electron beam imaging (EBI)), magnetographics, inkjet printing, screen printing, and thermal mass transfer. More detailed information concerning such methods is available in standard printing textbooks.
To date, many of the graphic films employed are PVC based films that typically combine good printability with desired properties in the graphics application including such properties as long term durability (e.g. several years), easy application, good adherence also to uneven surfaces including for example surfaces with rivets with minimal or no tendency of the film popping up. However, there is a desire to replace the PVC based films with non-PVC based film. Unfortunately, balancing the beneficial printing properties with desired properties in the graphics application have been proven difficult.
In particular in the case of non-contact printing methods, such as inkjet printing, it has been found difficult to find a film with a good balance of properties, yet inkjet printing is becoming a more and more popular printing technique to produce the graphics. In inkjet printing the individual ink drops are deposited on the surface. In order to achieve good image quality, the ink drops need to spread, join together, and form a substantially uniform, leveled film. Insufficient wetting results in low radial diffusion of the individual ink drops on the surface of the substrate (also referred to as “dot gain”), low color density, and banding effects (e.g., gaps between rows of drops).
Inkjet printing is emerging as the digital printing method of choice due to its good resolution, flexibility, high speed, and affordability. Inkjet printers operate by ejecting, onto a receiving substrate, controlled patterns of closely spaced ink droplets. By selectively regulating the pattern of ink droplets, inkjet printers can produce a wide variety of printed features, including text, graphics, holograms, and the like. Many of the inks used in inkjet printers are solvent-based.
Ink receptive media, in particular media receptive to solvent based inks used for example in inkjet printers have been disclosed in for example US 20030235681, WO 03/002353, US 20030224150 and US 20030107635. U.S. Pat. No. 6,869,496 discloses a non-PVC based film comprising a mixture of a first and second amorphous polyester. However, it has been found that the latter non-PVC film can be further improved relative to its ink receptive properties, in particular ink receptivity relative to ink jet printing where the ink is solvent based. Generally, the raw materials constituting this film are expensive and further, the manufacturing of the film will typically require an additional feeding station at the extruder, hence complicating manufacturing of the film.
It would now be desirable to find a further printable film that can in particular be printed with solvent based inks and in particular that can be printed with solvent based inks in inkjet printers including piezo inkjet printers. Desirably, such a film is a non-PVC based printable film and is of low cost, yet providing good to excellent printing properties. It would also be desired that the film can be produced in an easy and convenient way, hence contributing to a lower cost of the produced film. It would further be desirable to find a film that can be used for producing graphics, such as for example large graphics, that can be applied to vehicles or buildings for purposes of advertisement for example. Desirably, the graphic adheres well to these substrates yet can be easily and cleanly be removed. In particular, a printable film would be desired that has good or excellent mechanical properties. Desirably, the film can be adhered to uneven surface such as for example on surfaces including rivets and the film is not prone to or has limited popping up, i.e. showing detachment from the uneven surface. Desirably, the film has long term durability allowing the graphic to be used for an extended period of time, e.g. several years, in for example an outdoor application. Desirably, the printable films can be easily printed and can be handled and applied easily and conveniently.
In a particular aspect, the present invention provides a film having a polyester layer comprising a blend of amorphous polyester and a copolymer of an olefin and a hydrocarbon ester of an acrylic acid, wherein the amount of copolymer is at least 30 parts per 100 parts by weight of amorphous polyester and wherein the polyester layer exhibits an E-modulus at 23° C. of at least 200 N/mm2.
The term ‘polyester layer’ in connection with this application is merely used for sake of ease of understanding in designating the layer of the film comprising the amorphous polyester and the copolymer of an olefin and hydrocarbon ester of an acrylic acid without the intention to limit the composition of the layer. Accordingly, the polyester layer may contain additional components and the quantities of any of the components in the layer including the polyester can vary without the term polyester layer being intended to limit the composition of the layer.
The film is typically of low cost, yet provides good to excellent printability, in particular by solvent based inks Accordingly, for sake of convenience, the film may also be referred to hereinafter as printable film. The film can be printed well with inkjet printers including piezo inkjet printers using solvent based inks. In a particular aspect of the present invention, the polyester layer may be a self-supported layer and thus the polymeric film may consist of a single layer formed by the polyester layer. Hence, the first major side of the polyester layer defines the printable surface of the printable film and the surface on the opposite second major side of the polyester layer may be provided directly with an adhesive layer. Optionally, one or more primer layers may be provided between the surface of the polyester layer and the adhesive layer or the surface may be corona treated for improving adherence of the adhesive layer thereto.
In a further aspect, there is provided a method of making a graphic suitable for application on vehicles or buildings, the method comprising printing of an ink composition on the polyester layer of the film.
In yet a further aspect, there is provided a graphic comprising an ink composition printed on the polyester layer of the printable film.
In a still further aspect of the invention there is provided a method of applying a graphic comprising adhering the graphic to a vehicle or a building.